Your texture pack seems to have a fairly high definition, make sure you have gone to the video settingsand re-appropriated it to accommodate fps. It reset after the upgrade to 1.6 . Also, speaking of your texture pack, it seems to have a higher definition than that of the default. It could deter your frame rate.
If you have always had it like that, those are just a few things to check. Otherwise, my client seems to be boding quite well. You might need to relog some till the issue is resolved.